Question

How to write custom callback function to an array (apply a function to each element) in Swift

Answer 1

// Callback‑passing style similar to C, Go,

import Foundation

// Custom function that applies a callback to each element
func applyToArray(_ arr: [Int], callback: (Int) -> Int) -> [Int] {
    var result = [Int]()
    result.reserveCapacity(arr.count)

    for value in arr {
        result.append(callback(value))   // apply the callback
    }

    return result
}

// callback function
func square(_ x: Int) -> Int {
    return x * x
}

let numbers = [2, 4, 6, 8]
let squared = applyToArray(numbers, callback: square)

print(squared)   



/*
run:

[4, 16, 36, 64]

*/

 

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